Figure 1.
Phenotypic variation in herkogamy in different A. thaliana genotypes.
Freshly opened flowers of Col-0 (A), weak phenotype of BRA (B), strong phenotype of BRA (C), SIM (D), F1 hybrid of BRA and Col-0 (E), F1 hybrid of SIM and Col-0 (F), and F1 hybrid of SIM and BRA (G) under greenhouse conditions. Scale bar = 1 mm. (H) A flower of SIM showing weak approach herkogamy under natural conditions at high altitude. Parts of petals and sepals were removed to improve visibility in some flowers.
Figure 2.
Characterization of approach herkogamy in the greenhouse.
(A) Means with standard errors (SEs) of fertilization rates in Col-0, BRA, and SIM – upon autonomous selfing, assisted selfing, and pollination of a male-sterile line (pollen siring). Letters above bars indicate significant differences (Tukey's post-hoc significance tests, α = 0.05) within each fertilizing group. (B) Self-fertilization rates in successive siliques along the main stems of Col-0, BRA, and SIM. The regression function is: y = exp(a+b*x)/(1+exp(a+b*x)). Coefficients (a/b) of non-linear models are 0.89/0.33, −2.98/0.15 and −5.97/0.035 for Col-0, BRA and SIM, respectively. (C) Measurements of anther height (AH) and stigma height (SH) in flowers of Col-0 (flowers N = 20), BRA (N = 27), and SIM (N = 16) and their hybrids (F1_BRAxCol-0, N = 16; F1_SIMxCol-0, N = 20; F1_SIMxBRA, N = 13). Significant differences (one-way ANOVA) between AH and SH within each genotype are indicated in the white boxes. Letters above bars indicate statistically significant differences (Tukey's post-hoc significance tests, α = 0.05) in AH or SH across all examined accessions. (D) Calculated SAS (SAS = SH – AH; means± SEs) of Col-0, BRA, SIM and their hybrids.
Figure 3.
Herkogamy and its reproductive consequence under natural conditions.
Boxplots of SAS (the proxy of herkogamy, A) and outcrossing rates (OR, B) in BRA, SIM, and the control accessions growing in the field experiments (high and low altitudes). Significant differences are indicated. ***, P<0.001; *, P<0.05; n.s., P>0.05. Scatterplots and Pearson's correlation between SAS and OR in the field experiments (C) and the common-garden experiment (D). Means with standard errors are shown.
Figure 4.
The influence of ambient temperature on the expression of herkogamy.
Accession means of SAS (the proxy of herkogamy) in Col-0, BRA, and SIM plants grown under different ambient temperatures and identical light conditions are shown.
Figure 5.
Quantitative trait locus (QTL) analysis of approach herkogamy.
(A) Distributions and correlations of untransformed phenotypic data of SAS (the proxy of herkogamy), self-fertilization rate (FR), anther height (AH), and stigma height (SH) in an F2 population derived from a cross between SIM and Col-0. The R2 values based on Pearson's correlation are shown in the plots (all P<0.001). (B) Alignment of logarithm of odds (LOD) maps for SAS, FR, AH, and SH. The dashed lines indicate the genome-wide significance threshold at LOD 3.0. LG, linkage group.
Figure 6.
(A) Diagrams for approach herkogamy (left) and reverse herkogamy (right). Theoretically, SAS (the proxy of herkogamy) is determined by two main components, the vertical (Dv) and horizontal separation (Dh) between stigma and anther. (B) A representative flower of A. lyrata showing considerable separation between stigma and anther in both vertical and horizontal directions. The inset shows an A. thaliana Col-0 flower for comparison (parts of petals and sepals were removed to improve visibility). Scale bar = 1 mm.